As conventional methods of measuring the drowsiness and consciousness level of a subject without putting pressure on the subject, the method using the heart rate or a pulse wave signal are known. For example, a method is known in which the peak frequency of a heart rate signal during consciousness is used as a reference and the drowsiness level of a subject is evaluated according to whether the frequency of the heart rate signal of the subject is lower than the peak frequency. Furthermore, for example, a method is also known in which the consciousness level of a subject is evaluated according to the intensity of a low frequency part or a high frequency part of a pulse wave signal or the ratio between the low frequency part and the high frequency part.    Patent Document 1: Japanese Laid-open Patent Publication No. 2004-350773    Patent Document 2: Japanese Laid-open Patent Publication No. 8-299443